Hemispherx Biopharma Inc. (HEB), the maker of an injectable medicine for genital warts, failed for the second time to win U.S. approval for a drug to treat chronic fatigue syndrome. The Food and Drug Administration will require the company to conduct at least one addition clinical trial of the medicine, called Ampligen, complete various nonclinical studies and perform further data analysis, Philadelphia-based Hemispherx said yesterday in a statement. Those with chronic fatigue syndrome are plagued by severe, continued tiredness triggered by an unknown cause, according to the National Institutes of Health. An FDA advisory panel determined in December that Ampligen hadn’t been proven effective. The agency’s staff raised questions about the company’s lack of safety data on the drug. The FDA rejected the treatment in 2009 and requested more data on its effectiveness. “The agency stated that the submitted data do not provide substantial evidence of efficacy of Ampligen for the treatment of CFS and that the data do not provide sufficient information to determine whether the product is safe for use in CFS,” Hemispherx said in its statement.